A 91-year record of seasonal and interannual variability of diatoms from laminated sediments in Saanich Inlet, British Columbia

Diatom seasonal succession and interannual variability were studied using laminated sediments from Saanich Inlet, British Columbia, for the years 1900-1991. Frozen sediment cores allowed fine-scale sampling of laminae for each year. Thus, three 'seasons' for each year were identified based on species composition. Thalassiosira species were indicators of spring deposition. Skeletonema costatum was abundant in samples following Thalassiosira, probably deposited in late spring and summer. Rhizosolenia sp. was most abundant in fall/winter samples. Diatom stratigraphies were related to sea surface temperature, salinity, sea level and the Pacific North American Index (PNA) using canonical correspondence analysis (CCA). CCA showed that species of a particular season generally had optima for temperature and salinity characteristic of that time. Interannual changes in diatom species composition and abundance were most prevalent in the decades 1920-1940, with the exception of S.costatum which showed cyclic changes in abundance. Skeletonema was more abundant during periods of cool temperatures, while littoral diatoms were more abundant during times of heavy winter rains. Sea level was an important variable in CCA and while its relationship to diatoms is not clear, it may be related to variations in nutrient supply to diatoms in surface waters.